Distribution of full motion video data has evolved from early television broadcasting to meet viewer demand. Recently, several different wideband digital distribution networks have been proposed for offering subscribers an array of video services, including true Video On Demand service. The following U.S. patents disclose representative examples of such digital video distributions networks: 5,253,275 to Yurt et al., 5,132,992 to Yurt et al., 5,133,079 to Ballantyne et al., 5,130,792 to Tindell et al., 5,057,932 to Lang, 4,963,995 to Lang, 4,949,187 to Cohen, 5,027,400 to Baji et al., and 4,506,387 to Walter. For example, Litteral et al. U.S. Pat. No. 5,247,347 discloses a digital video distribution network providing subscribers with access to multiple Video On Demand service providers through the public switched telephone network.
The prior art video networks have not addressed many problems which arise when the networks must be adapted to provide end users with equal access to multiple video information providers. The networks of the prior art also typically have not been designed to accommodate a full range of digital services such as telephone, video, video-on-demand, data services, information services, interactive services, and other modern digital offerings.
A disadvantage of systems such as that of Litteral et al., which use the PSTN as a video distribution system is that they are often bandwidth limited. Because the systems use the PSTN only for connectivity between subscribers and/or between subscribers and Video Information Providers (VIPs), there is no capability for dynamic routing of digitized video without requiring dedicated leased, wide bandwidth circuits. Also, point-to-point connectivity makes it difficult to offer a wide array of broadcast services such as are now widely available through existing CATV systems.
Attempts have been made to improve the core switching, multiplexing and transmission technologies for integrated digital networks to support voice, data and video services from VIPs for multiple users. For example, fiber optic transmission systems with bandwidths ranging from 155.52 to 2,488.32 Mbps have been considered to improve bandwidth access. In addition, asynchronous transfer mode (ATM) has been developed as a technique to provide broad-bandwidth, low delay, packet-like switching and multiplexing. In ATM, usable capacity can be assigned dynamically (on demand) by allocating bandwidth capacity to supply fixed-sized information-bearing units called "cells" to point-to-point or multi-point outputs. Each cell contains header and information fields. The ATM standard, CCITT.121/2 specifies a 53 byte cell which includes a 5 byte header and a 48 byte payload.
MPEG (motion picture experts group) is a broad generic standard for digital video program compression. A number of specific compression algorithms satisfy MPEG requirements. MPEG-2 is a second generation compression standard capable of encoding video program material into a 6 Mbits/sec bit stream and packetizing a number of 6 Mbits/sec channel streams into a single higher rate signal transport stream. The conversion of MPEG-2 data into ATM cell format, however, imposes additional overhead requirements that reduce the information-carrying capacity of the network. For example, synchronous transmission protocols, such as SONET, may require a stream of continuous data to retain synchronization. Thus, an ATM data stream carrying MPEG video data that is transmitted on a synchronous carrier may need to be padded with ATM idle cells, or "dummy cells", in order to ensure proper synchronization with the physical layer. Therefore, the network's information-carrying efficiency is reduced each time information data is converted to another layer of transport protocol.
In addition, there has been a growth of VIPs offering video services to subscribers. The growth in the number of VIPs offering services will result in capacity problems on the PSTN connecting the VIP services to their subscribers. In addition, any one VIP may not fully utilize the physical connection to the PSTN when providing video services. Thus, if a plurality of VIPs each use an assigned optical fiber at, for example, fifty percent capacity, the PSTN will be inefficiently utilized if the optical fiber of each VIP is connected to the PSTN internal switches. Thus, a need exists for increased bandwidth and efficient connectivity techniques in the PSTN as competition increases between VIPs for connectivity to subscribers.
An example of a video network utilizing a Level 1 Gateway is disclosed in commonly-assigned copending application Ser. No. 08/304,174, filed Sep. 12, 1994 now U.S. Pat. No. 5,682,325, the disclosure of which is incorporated herein in its entirety by reference. FIG. 1 corresponds to FIG. 4 of this commonly-assigned copending application and discloses a hybrid fiber-coax system which provides RF transport of both analog and digital broadband services. The illustrated network provides broadcast video distribution, archival video services and interactive multi-media services as well as plain old telephone service.
The network of FIG. 1 includes a Loop Transport Interface 10 located in a telco central office. In an area serviced through multiple central offices, several different central offices would each have a Loop Transport Interface similar in structure to the Interface 10 depicted in FIG. 1. In some respects, each Loop Transport Interface serves as the headend of an otherwise conventional optical fiber trunk and coaxial cable type CATV distribution network.
In the Loop Transport Interface 10, a laser type optical transmitter 12 transmits downstream signals through fibers 14 to optical to electrical nodes referred to as "optical network units" or ONU's. The laser operates in a linear mode in the range of 5-750 MHz. The transmitter 12 is followed by an optical splitter that can transmit to several ONU nodes 16. Each ONU 16 performs optical to electrical conversion on the downstream signals and supplies downstream RF electrical signals to a coaxial cable distribution system 18.
The optical transmitter receives and transmits signals from an RF (radio frequency) combiner 20. The combiner 20 combines levelized RF signals from several sources to produce the appropriate signal spectrum for driving the optical transmitter 12. One set of signals supplied to the RF combiner 20 are group of AM--VSB (amplitude modulated vestigial sideband) analog television signals 22 from one or more appropriate sources (not shown). Such signals are essentially "in-the-clear" CATV type broadcast signals capable of reception by any subscriber's cable ready television set.
The analog television signals are broadcast from the optical transmitter 12 through the tree and branch optical and coax distribution network to provide "basic" CATV type service to all subscribers on the network. In order to obtain additional network services as discussed below, the subscriber may obtain a digital entertainment (DET) 24. A network interface module in the DET 24 includes a tuner that permits subscribers to the digital services to receive the analog broadcast channels through the same equipment used for the digital services.
The network depicted in FIG. 1 also provides transport for digitized and compressed audio/video programming, both for certain broadcast services and for interactive services, such as video on demand. The network uses a video compression called Motion Picture Experts Group (MPEG). The MPEG encoded video is transported to each Loop Transport Interface using asynchronous transfer mode (ATM) transport and switching.
In the illustrated network, digital broadcast service signals 26 in MPEG encoded form and arranged in ATM cell packets are applied to an ATM packet handler 28 in the Loop Transport Interface 10. These broadcast service signals 26 originate in one or more broadcast VIP's ATM encoders, controlled by the VIP's servers. The ATM broadcast services carry premium service type programming. For certain interactive services which utilize one digitized channel to provide limited downstream transport to a large number of subscribers, the ATM broadcast cell stream signals originate from a server 30. Fully interactive broadband digital signals, in MPEG-ATM format, are also applied to the ATM packet handler 28 from an ATM switch 32. The ATM packet handler 28 terminates all ATM cell transport through the network, and converts the cell payload information into MPEG-2 format bit streams.
In addition to the analog broadcast signals, the RF combiner 20 receives a variety of other analog RF signals from a group of RF digital modulators 34 that output the MPEG streams from the ATM packet handler 28 as digital broadband information in RF analog format. Each RF modulator 34 outputs a 6 MHz bandwidth IF signal which an upconverter (not shown) tunes to a different RF channel having a corresponding carrier frequency. A network controller 36 and an associated network data processor (NDP) 38 use the VPI/VCI header from the ATM cells to control the ATM packet handler 28 to route the MPEG bit streams to the appropriate digital RF modulator 34.
The RF modulators 34 use 64 QAM (quadrature amplitude modulation) or 16 VSB (vestigial sideband) modulation techniques. The 64 QAM is used to modulate 4 channels of 6 Mbits/s MPEG encoded digital video information into one 6 MHz bandwidth analog channel. Similarly, 16 VSB modulates 6 channels of 6 Mbits/s MPEG encoded digital video information into one 6 MHz bandwidth analog channel. As another example, U.S. Pat. No. 5,231,494 to Wachob, the disclosure of which is incorporated herein in its entirety by reference, teaches quadrature phase shift keyed (QPSK) modulation of a plurality of video, audio and data signals into a single data stream within a standard six MHz channel allocation for transmission over a CATV type distribution network.
The 6 MHz bandwidth RF signals from the modulators 34 are supplied to the optical transmitter 12 for downstream transmission together in a combined spectrum with the AM-VSB analog television signals 22. The downstream transport of the digital programming is an RF transmission essentially the same as for the analog basic service channels, but each of the channels from the RF modulators 34 contains 4 or 6 digitized and compressed video program channels, referred to hereinafter as "slots". The 6 Mhz digital program channels are carried through the fiber and coaxial system in standard CATV channels not used by the analog basic service programming. The ONU 16 is essentially transparent to both the analog basic service channels and the channels carrying the digital programming and supplies all of the signals as a combined broadcast over the coaxial cable network 18.
At the subscriber premises, a network interface module (NIM) (not shown) couples the set-top device or digital entertainment terminal (DET) 24 to a drop cable of the coaxial distribution network 18. In this network configuration, the NIM includes an analog frequency tuner controlled by a microprocessor to selectively receive the RF channel signals, including those channels carrying digital information. The NIM also includes a QPSK, QAM or VSB demodulator to demodulate a selected one of the digitized program signals carried in one of the digital slots within a received 6 MHz channel and performs a forward error correction function on the demodulated data. A digital audio/video signal processor within the DET decompresses received video signals, generates graphics display information and performs digital to analog conversion to produce output signals compatible with a conventional television set 40.
The analog tuner in the NIM tunes in all channel frequencies carried by the network, including those used for the analog broadcast services. The DET 24 includes a bypass switch and an analog demodulator to selectively supply analog signals from the basic service channels directly to the audio/video output terminals or to the modulator, to provide signals to drive a standard television receiver.
The DET 24 also includes a remote control and/or keypad to receive various selection signals from a user. The DET relays data signals upstream over a QPSK signaling channel on the coaxial cable to the ONU 16 in response to user inputs such as selection of a pay per view event. The actual transmission of any such data signals upstream from the DET 24 occurs in response to a polling of the DET. The ONU 16 combines upstream data signals from the DET's serviced thereby and transmits those signals upstream over another optical fiber 42 to an optical receiver 44 in the Loop Transport Interface 10. Each DET 24 may transmit data on a different carrier frequency, in which case the network controller 36 knows during the polling process which DET sent particular data based on the received frequency channel. Alternatively, for interactive services, the DET may transmit a unique identification code with the upstream message.
In the implementation of the network illustrated in FIG. 1, an ACC 4000D 46 performs set top management and specific program access control functions. In particular, service profiles for each customer on the network and their DET's are set up and stored within the Level 1 Gateway 48. The Level 1 Gateway 48 may also provide an interface to appropriate billing systems (not shown) for some broadcast services, such as pay per view.
For ATM broadcast services, when a subscriber first signs up, a portfolio of channels subscribed to by that customer is established in the subscriber's profile data within the ACC 4000D 46. Based on this profile data, the ACC 4000D 46 downloads a service map into the subscriber's DET 24. The downstream transmission portion of the network provides an out-of-band downstream signalling channel to the DET's, for example for the downloading of the service map information from the ACC 4000D 46 to each DET 24. This downstream signaling channel also carries signals for controlling software downloading and/or selection of certain channels or frames for decoding in interactive services.
All digital broadcast service signals are broadcast into each subscriber's premises, and each DET 24 includes means for receiving and decoding each such digital broadcast service channel, which may include premium channels. The microprocessor in the DET 24 controls access to any of these channels based on the downloaded map information stored in the system memory. For example, if one subscriber requests HBO, and that subscriber has paid to subscribe to HBO, the subscriber's DET 24 contains map information instructing it to tune to the RF channel and select and decode the digital program slot carrying HBO for display on the subscriber's television set 40. However, if a requesting subscriber has not paid for HBO, the downloaded service map will not provide the requisite data for tuning and decoding of that channel. If a decryption key is needed, the Level 1 Gateway 48 instructs the video manager 50 to instruct the ACC 4000D 46 to transmit the key to subscriber's DET 24.
The implementation of the network illustrated in FIG. 1 also provides telephone service. Between the optical network unit and the subscriber premises, the 700-750 MHz portion of the spectrum on the coaxial cable carries the telephone signals. This allocated spectrum provides transport for 24 DS0 telephone channels. Each subscriber premises has telephone interface referred to as a Cable Network Unit (CNU) 52 coupled to the coaxial cable which serves to couple two-way signals between a twisted wire pair into the home and the telephone frequency channels on the coaxial cable 18. Upstream telephone signals are applied from the optical receiver 44 to a host digital terminal (HDT) 54 which provides an interface to a standard digital telephone switch 56. Downstream telephone signals from the switch 56 pass through the HDT 54 to the RF combiner 20 for transmission in the 700-750 MHz frequency range over the fiber to the ONU 16 and the coaxial cable distribution system 18. Upstream telephone signals are output in the 5-40 MHz frequency range of the coaxial cable, which are block converted in the fiber nodes for transport on an optical fiber.
The implementation of the network illustrated in FIG. 1 also offers access to video information providers (VIP's) for interactive broadband services, such as video on demand. For archival services and many other interactive services, each VIP has a level 2 gateway and some form of broadband information file server 403. The ATM switch 32 provides communications links between the Loop Transport Interfaces 10 and the level 2 gateways and file servers 60. Customer access to the VIP's is controlled through one or possibly more programmed computer or processor elements performing the processing functions of the Level 1 Gateway 48. A permanent virtual circuit (PVC) controller 56 and a video manager 50 respond to signals from the Level 1 Gateway to control the point to point routing through the network.
The PVC controller 56 stores data tables defining all possible virtual circuits through the ATM switch 32 and the Loop Transport Interface 10 serving each DET terminal of a customer subscribing to each particular provider's services. These data tables define the header information and the switch port to the packet handlers needed to route cells to the correct Loop Transport Interface. The video manager 50 stores similar data tables identifying the transmission fiber ports, RF channels and multiplexed digital channel slots which may be used to transport each data stream processed by the ATM packet handler 28 through the fiber 14 to the appropriate ONU 16 serving each DET. The data tables in the PVC controller 56 and the video manager 50 thus define "permanent virtual circuits" between the VIP's equipment 403 and the DET's 24.
For a full, broadband interactive session, the subscriber operates the DET 24 to interact with the Level 1 Gateway 48 and select a VIP. The PVC controller 56 responds to instructions from the Level 1 Gateway by activating the ATM switch 32 to establish a downstream virtual circuit path between a port of the VIP's server and the ATM packet handler within the Loop Transport Interface 10 servicing a subscriber requesting a call connection to the particular VIP. The video manager 50 assigns a particular one of the digitized video channel slots in a digital program type RF channel to carry the particular point to point communication. Specifically, the video manager controls the ATM packet handler 28 to route MPEG data recovered from the ATM cells for the particular point to point communication to the port for one of the RF modulators 34 so that the modulator will include the MPEG data in the assigned digital channel slot within a particular 6 MHz RF channel. The video manager 50 also transmits a signal downstream through the signaling channel to the subscriber's DET 24 instructing the DET to tune to the particular RF channel and decode MPEG data from the specifically assigned digital channel within that RF channel. Similar dynamic assignments of RF channels on a CATV system to individual terminals for interactive services are disclosed in U.S. Pat. No. 5,220,420 to Hoarty et al. and U.S. Pat. No. 5,136,411 to Paik et al., the disclosures of which are incorporated herein in the entirety by reference.
Concurrently, the Level 1 Gateway 48 would instruct the PVC controller 56 to control the ATM switch 32 to establish an upstream virtual circuit for control signals sent from the DET 24 up through the fiber-coax network and receiver 44 to the VIP's level 2, gateway.
While the network disclosed in FIG. 1 is able to provide broadcast video and interactive video services to video subscribers, the overall architecture is limited in that the loop transport interface 10 is able to service only a limited number of living units, for example approximately 2,000. Thus, if it is desired that full-service digital broadband video services are to be provided to a greater population, a substantial expenditure must be invested to install additional loop transport interfaces throughout proposed video service areas. Since the costs for installing and implementing the additional loop transport interfaces 10 may be substantial, a network provider may be hesitant to invest substantial capital for new equipment necessary for the additional loop transport interfaces if the new subscribers in the proposed video service areas are willing to pay only a limited amount of subscriber fees.
In addition, the network disclosed in FIG. 1 requires a substantial amount of control processing and connectivity with the video information providers and the corresponding servers 60. If additional loop transport interfaces 10 are to be added to proposed service areas, the VIPs may be required to communicate with multiple level 1 gateway controllers 48 from the different service areas, creating additional difficulties in management and service processing for the VIPs.